U.S. Pat. No. 3,257,448 discloses producing carboxylic acid esters by liquid phase oxidation of a mixture of an alcohol and an aldehyde, using a mixture of palladium chloride and copper chloride as catalyst. Large amounts of lithium salts are required as binding agent for the water thus produced. The catalyst system is very complex and difficult to handle.
U.S. Pat. No. 3,639,449 discloses a process by which alcohols or mixtures of alcohols and aldehydes are oxidized to esters in the liquid or gaseous phase at an elevated temperature by molecular oxygen in the presence of heterogeneous noble metal catalysts. Activated carbon and diatomaceous earth are used as support material when the reaction is done in the liquid phase. Since noble metal catalysts are expensive and the catalysts undergo loss of metal during use owing to mechanical abrasion, the losses are of great economic significance. In a subsequent publication, Chem., Abs, vol. 79 (1973):4594a, the inventor of U.S. Pat. No. 3,639,449, reported that, in the liquid phase, aldehydes inactivate the catalyst because of their strong affinity for the catalyst. Because aldehydes are produced in all cases of oxidation of alcohols, such a catalyst can not be used over a prolonged period of time.
It is an object of the present invention to provide a process using an inexpensive and effective catalyst system, which is not affected by catalyst abrasion.